1. Field of the Invention
This invention relates generally to turbomachine vanes and blades and, more particularly, to a method for fabricating transpiration cooled vanes and blades.
2. Description of the Prior Art
U.S. Pat. No. 3,606,573 issued to Emmerson et al on Sept. 20, 1971 and assigned to the assignee of this invention, describes a porous metal panel. U.S. Pat. No. 4,042,162 issued to Meginnis et al on Aug. 16, 1977 and assigned to the assignee of this invention, describes a method of fabricating a transpiration cooled turbine blade for a gas turbine engine. The blade has a hollow, airfoil-shaped spar which forms the structural part or backbone of the blade and a sheath of porous metal around the spar which forms the outer surface of the blade exposed to radiant heat and/or hot gas products of combustion. As described in the aforesaid U.S. Pat. No. 4,042,162, the sheath of porous metal is fabricated separately and diffusion bonded to the spar with pores in an inner surface of the sheath aligned with passages through the spar wall. The spar wall passages conduct gaseous coolant from a plenum chamber behind the spar wall to the pores. In diffusion bonding the sheath to the spar, referred to herein as hot isostatic press bonding or HIP bonding, very high pressure is applied to the outer surface of the sheath as the latter and the spar are heated to high temperatures. A major concern is preventing collapse or distortion of the spar during HIP bonding.
U.S. Pat. No. 3,623,204 issued to Wagle on Nov. 30, 1971 and assigned to the assignee of this invention, describes a method of fabricating a hollow turbine blade wherein sealed gas containers are disposed within the interior of the blade and then pressurized to force the outside surface of the blade against the inside of a die chamber. The spar is reinforced against the gas pressure forces by the surface of the die chamber. In the aforesaid U.S. Pat. No. 4,042,162, the passages in the spar wall are formed before the sheath is attached so that reinforcement of the spar wall during HIP bonding from within the blade requires a casting core or like arrangement. A method according to this invention of fabricating a transpiration cooled turbine blade or vane or other flow directing element incorporates improved and simplified steps for achieving spar wall reinforcement during HIP bonding.